1. Field of the Invention
The present disclosure relates to an emergency core cooling system and an emergency core cooling method for a water-cooled reactor system, and more particularly, to an emergency core cooling system and an emergency core cooling method for a fail-safe water-cooled reactor, which completely removes decay heat generated from a core in safety while an active component such as a pump is not used.
2. Description of the Related Art
Doubts of the general public about safety of a nuclear power plant have been significantly increased due to the nuclear accident occurring in Fukushima, Japan, on Mar. 11, 2011, and thus various countermeasures improving safety of an existing nuclear power plant have been provided.
Meanwhile, most nuclear reactors of nuclear power plants throughout the world as well as the nuclear reactor of the nuclear accident occurring in Japan are water-cooled reactors. In the water-cooled reactor, water is used as a coolant of a core, and examples thereof include a pressurized water reactor, a pressurized heavy water reactor, and a boiling water reactor.
The most important object to be solved in order to increase safety of the water-cooled reactor is to effectively remove decay heat continuously generated even after the nuclear reactor is shut down due to radioactive decay of nuclear fission products when the nuclear reactor is shut down.
To this end, in the water-cooled reactor, an emergency core cooling system (ECCS) for removing decay heat after the nuclear reactor is shut down is provided to cope with the case where a loss of coolant accident (LOCA) occurs or water is not supplied through a main feedwater system or an auxiliary feedwater system due to an accident.
An emergency core cooling system of a commercial nuclear power plant is generally constituted by a safety injection tank, a safety injection system, and a recirculation system. The safety injection tank passively supplies water stored in a compression tank into a reactor vessel by using a pressure difference when the loss of coolant accident occurs. In addition, the safety injection system actively supplies cooling water from an in-containment refueling water storage tank into the reactor vessel by using an active component such as a pump. In addition, when water of the in-containment refueling water storage tank is used up, the recirculation system supplies back cooling water collected in a recirculation sump provided on the bottom of a containment into the reactor vessel by using the pump.
As described above, since the emergency core cooling system of the commercial nuclear power plant has a limited cooling water volume of the safety injection tank, an active system using the pump as well as a passive system is necessarily required to cool a core over a long period of time. However, when a nuclear accident accompanied by a station blackout (SBO) where electric power supply is cut off over a long period of time occurs, the active system of the emergency core cooling system cannot be used, accordingly, the core cannot be cooled over a long period of time.
Therefore, in the case where emergency core cooling is required, a passive emergency core cooling system needs to be developed, which can completely remove decay heat generated from the core in safety while the active component such as the pump is not used and the core is not exposed.
See Korean Patent No. 813,939 and Korean Patent No. 1,242,746 for related art documents.